Wireless power transfer is a well-known type of power transfer permitting the transmission of electrical power from a power source to a consuming power device without using conductors. Wireless power transfer can comprise, for example, inductive power transfer in which time-varying electromagnetic fields are typically transmitted across an air gap to the consuming device. The power is transferred through induction which relies on a magnetic field generated in a transmitter (or primary coil) by an electric current to induce a current in a receiver (or secondary coil). This is the action employed in, for example, a transformer where the primary coil and secondary coil are not connected.
Wireless power transfer also comprises energy harvesting to convert ambient energy from the environment to electric power. The ambient energy may come from stray electric or magnetic fields or radio waves from nearby electrical equipment.
In all forms of wireless power transfer, there is a need for an improved rectifier. For example, in inductive power transfer applications where the primary and secondary coils are not in close proximity and therefore do not have a high coupling factor, there is a need for more efficient, powerful and/or high frequency resonant rectifiers.